Noise dosimeters have been used extensively over the past two decades to document personal exposures to noise and to assure workplaces comply with permissible noise exposure levels. The Specification for Personal Noise Dosimeters (S1.25-1991 (R2001)) of the American National Standards Institute (ANSI), states that dosimeters should be suitable for measurements of impulsive, intermittent, and continuous noise.
Current noise dosimeters typically measure noise levels (average, maximum, minimum, and peak), noise dose, projected noise dose, and sound exposure level. The Occupational Safety and Health Administration (OSHA) Noise Exposure Standard, set forth in 29 C.F.R. § 1910.95, requires personal exposure to noise to be measured as a noise dose over a work day. Total noise dose, D, over a work day is calculated according to the following equation:D=100×[C1/T1+C2/T2+ . . . +CN/TN],  (Equation 1)where CN is the total time of exposure (in hours) at a specific noise level, and TN is the allowable exposure duration at the measured A-weighted slow sound level, LAS. TN is computed by the equationTN=8/2(LAS−90)/5  (Equation 2)
This manner of computing dose is based on the assumption that halving the exposure time to a noise level creates the same degree of hazard to hearing as reducing the noise level by a specified amount (referred to as an “exchange rate”), and that doubling the exposure time creates the same degree of hazard as increasing the noise level by the same amount. The OSHA standard, expressed in Equation 2, applies an exchange rate of 5 (dBA(the National Institute for Occupational Safety and Health recommends an exchange rate of 3 dBA). Applying Equation 2, an exposure of 90 dBA for four hours is considered to be equivalent to either (1) an exposure of 85 dBA for eight hours, or (2) an exposure of 95 dBA for two hours.
Although the foregoing method of computing dose has proved reliable for continuous noise levels, dose calculated by this method does not accurately represent the potential risk of an impulse event. For example, using Equations 1 and 2 above, an impulse generated by a single gun-shot in an indoor firing range can contribute as much as 106% to 158% of the daily allowable dose.
Further, current state-of-the-art noise dosimeters have a sound pressure level (SPL) dynamic measurement range of about 80-146 dB. Although this may be adequate for some impact noise environments, current state-of-the-art noise dosimeters cannot accurately measure impulse noise levels above 146 dB, such as impulse noise levels produced by weapons and certain construction equipment. When a dosimeter is used to measure an impulse noise level greater than its dynamic range, the dosimeter “clips” the noise level at the upper end of its measurement range.
Accordingly, there exists a need for new and improved systems for measuring and assessing noise exposure in an environment containing impulse noise.